Our invention relates to a process for making thin molybdenum sulfide films having a wide range of properties and, more particularly, to a process for making a molybdenum sulfide film having a thickness between several hundred to 5000 .ANG. and to the molybdenum sulfide films made therefrom.
The manufacture of molybdenum sulfide film is known. Different processes for making targets made of pressed molybdenum disulfide powder by cathodic RF sputtering have been described. However great disadvantages are connected with the use of this technique. It has been established by Mikkelsen, et al, Apply. Phys. Lett. 52(14), 1130(1988), that the films obtained by RF-sputtering have a very greatly reduced density compared with crystalline Molybdenum sulfide, since the material made in this way is very disordered in its crystalline structure and has a high proportion of impurities.
The physical properties of the film are clearly poor in contrast to molybdenum sulfide. The density of these films can be increased to the value of the cyrstalline material by an aftertreatment (400 kV Argon Ion Bombardment). The enormous power densities required limit these manufacturing methods to a few materials. Considerable contamination of the films by water which has a negative influence on the physical properties has been reported. This is because the cathodes must be cooled in order to prevent heating of the target so that residual water can condense; among other things the Molybdenum disulfide powder of the target takes up water, since it is hygroscopic in the powder finely-divided state. These problems are practically excluded by the In situ production of Molybdenum sulfide according to the process of out invention. An additional disadvantage of the described process is that it is difficult to attain a sufficient adherence on the substrate material. To accomplish sufficient adhesion frequently adhesion promotors or glue layers must be used.
The range of application of the known process is limited so that in sputtering processes extraordinarily sensitive substrates such as aluminum oxide ceramics, aluminum nitride, ceramics or noble steel can not be coated without problems. Likewise materials sensitive to higher temperatures such as Teflon, Polyimide, Epoxy resin or other plastic materials can not be used because of the high energy densities.
It is an object of our invention to provide strongly adhering thin layers of molybdenum sulfide of variable composition on any substrate. The electrical and triboelectric properties of these films are variable within a wide range and can be set to any desired value. The semifinished products so made are used in vacuum engineering, air and space vehicles, street and rail traffic control and in machine engineering. Use of layers, particularly for dry lubrication of bearings and sliding surfaces, which are subjected to extreme thermal stress, since the thermal resistance of these layers is very high.
Because of their catalytic properties the layers can be deposited on suitable supporting materials, also they can be used in the chemical industry as catalysts. Moreover use of molybdenum sulfide films in sensor engineering is of interest because of the electrical and chemical properties.
The electrical and optical properties of Molybdenum sulfide films open up the possibility applications in microelectronics and electrooptics.
The use of molybdenum sulfide films made with RF sputtering engineering of these applications is possible because of the previously named properties only with limitations regarding the band structure and the state densities. Since the electronic properties of the materials strongly perturbed in their crystalline structure are not adjustable, their use in microelectronics and electrooptics has not been possible previously.